6TL batteries not fully charging

[Caflin]

I just picked up my M35a3 a little over a week ago. On Friday I added some distilled water to the batteries as needed and charged them but couldn't get them past 12.2V. I was able to start the truck and I let it run for a little while. Later that night it fired up no sweat again. Tried it today and it didn't get close to starting.

The batteries are not getting a full charge and appear to not be holding a charge. I did some reading on desulfators (chargers, solargizers etc). Would a charger with a desulfating function like the BatteryMINDer model 2012 help bring these batteries back? Should I just replace them with new group 31s? Other recommendations?

 

[tennmogger]

Older and/or unused batteries tend to get higher resistance cells. This tends to let the voltage rise much higher across the batteries to achieve a usable charge. The fact your batteries never went over 12.2 V, which as you said does not charge them, sounds like a problem with the charger, not the batteries.

Try another charger? To have any idea if charging is taking place you must know the actual measured charge current through the battery and voltage across the battery. Can you measure the current?

The spec I found online indicated 225 AH for one brand of 6TL battery. You must therefore put at least that much into your dead battery to know if it's charging or not.

Some chargers would take a LONG time. Let's say a 6 Amp battery charger managed to average 3 amps into the battery, you'd have to charge for 70 hours, plus another 20% or so for inefficiencies. If you can charge them at least hard enough to create a little temperature rise you are doing good.

It would be a shame to trash those batteries.

Bob

 

[theeDIZ]

Have you checked your alternator to make sure it's charging ?

 

[rustystud]

Like was previously mentioned could be your charging system or your batteries have started to sulfate. I would charge the batteries separately out of the truck with a good known battery charger. If they are not coming up to 14 volts then you have bad batteries and I would get new ones. Don't waste your time trying to "revive" them. They'll only leave you "high and dry" sometime later . If it's your charging system then you'll need to start diagnosing it using the TM's. Usually it's either the regulator or diodes in the alternator, but you still need to go through the diagnostic checks just in case it's some wiring that is open or shorting to ground or something else that will cost you your new alternator again ! I've seen this happen too many times. Some mechanic will "assume" it's the regulator or whole alternator and after installing a new one on the truck will in short order fry the new regulator or alternator since the REAL problem is something else entirely different.

 

[rosco]

On a "New to You" truck, I'd start cleaning battery terminals & grounds to frame & block. I don't care how good they look.... poor connections will will cause the same problems!

 

[orren]

Also, I strongly suggest using a battery shut off switch. Seems these trucks leak voltage just standing around.
I've had that problem and still after several attempts can't find anything.

 

[Caflin]

Just as a follow up (hopefully helps someone on a future search). I charged the batteries seperately using a BatteryMINDer model 2012. The charger told me the one battery had a bad cell and even the "good" one wouldn't fully charge. So I bought a set of Deka Group 31 batteries. Starts great now.

Thanks for everyone's help.

 

[tobyS]

New is good.

Put your old ones on the charger and leave them for a few days. Then unhook and let them set for a couple more. If they fall below 12.5-12.7 volts then forget them, take them in for salvage or exchange.

I use the good ones for less demanding vehicles, like my F600 and they work great. One went to the dump trailer. In ten trucks bought, about 1/2 are reclaimed. My 005 generator liked 2 of them with a new bat. box. Golf cart is next (4).

As I resell most of my military vehicles, new batteries are always a good selling point. I use the 1400 cca bus batteries from O'reilly.

 

[KansasBobcat]

This may have been mentioned but load test. That will tell you real quickly if you need to replace.

 

[rustystud]

I would do like tobyS said and charge them up again. Then I would put a load on them and completely drain them. Then charge them up again and then test them. Some times this will bust off the sulfation that has built up on the plates. It is worth a try. Then you will have some decent spares to play with.